Signal Delay Circuit

[Radardude]

I have a tankless water heater and a water solar system. I'm designing a circuit to delay the tankless heater from turning on allowing the hot water to reach the tankless heater. A signal from the internal flow sensor activates the tankless heater. IC1 is a retriggerable monostable multivibrator. The IC1 output pulse is longer the than slowest signal freg. R2 and C2 will provide the delay of the signal through IC2. My question, is there a simpler way to do this or a better way?

[tszaboo]

My question, is there a simpler way to do this or a better way?

If you are going to fool yourself that putting an RC on a digital signal is a good solution, at least put a schmitt trigger input part after it.

[dannyf]

My question, is there a simpler way to do this or a better way?

1. 555 timer, or
2. mcu.

[Radardude]

My question, is there a simpler way to do this or a better way?

If you are going to fool yourself that putting an RC on a digital signal is a good solution, at least put a schmitt trigger input part after it.

Pin 1 of IC2 is like a switch, it will slowly charge up (about 60 secs) until it is seen as a high allowing the signal on pin 2 to pass out of pin 4. Pin 1 will remain high as long as the water is flowing. So I don't think I need a schmitt trigger. Timing of the signal is not important. I'm trying to keep the component count as low as possibly.

[electronics man]

I think an mcu is the best idea as you can easily experiment whith different times. You could use a 555 time but it is more difficult to experiment whith diferent times mcu is just the easiest. All you need is a cheep small mcu like picaxe 08 if you don't have another one in your BOM or you could use any mcu you want.

[Radardude]

I think an mcu is the best idea as you can easily experiment whith different times. You could use a 555 time but it is more difficult to experiment whith diferent times mcu is just the easiest. All you need is a cheep small mcu like picaxe 08 if you don't have another one in your BOM or you could use any mcu you want.

At first when you suggested to use a MCU I thought that was such an overkill. I have used Basic Stamps and Basicx BX24p on several elaborate projects in the past. But I didn't realize that such small and inexpensive MCU existed. I will use this MCU because of the small packaging and the small learning curve involved. It will provide a smaller component count than my design. This information opens up another wave of projects for me. Thanks for sharing.

[Skimask]

PIC10F200

[calexanian]

How about just a standard time delay relay. Nice, cheap, ready to go, and reliable. Amazon has many upon manys of them.

[Radardude]

How about just a standard time delay relay. Nice, cheap, ready to go, and reliable. Amazon has many upon manys of them.

I don't have the space for a time delay relay. It would still require additional components because the flow sensor signal (1hz to 100hz 0 to 5V) which is the activating signal.